12 



BULLETIN" 202, U. S. DEPARTMENT OF AGRICULTURE. 



RESULT OF MIXING SOUR AND NORMAL MILK. 



Since a positive alcohol test may be produced by increasing the 

 acidity, several investigators have pointed out that a mixture of sour 

 and normal milks will give a positive test. The amount of sour milk 

 which can be added to fresh milk without causing a positive alcohol 

 test will, of course, depend upon the acidity of the sour milk. In 

 one experiment, the results of which are shown in Table 7, various 

 percentages of sour, raw, and pasteurized milk were added to fresh 

 milk. The addition of 1 per cent of sour milk caused a positive test 

 with 75 per cent alcohol, 2.5 per cent caused a positive test with 68 

 per cent alcohol, and the addition of 10 per cent of sour milk was 

 necessary to cause a positive test with 44 per cent alcohol. 



It must be taken into consideration in this experiment that the 

 sour milk had a high acidity. If the acidity had been low a much 

 higher per cent could undoubtedly have been added to the fresh 

 milk without increasing the acidity sufficiently to cause a positive 

 alcohol test. 



Table 7. — The alcohol test with a mixture of normal and sour milk. 



Addition of sour raw milk. Acidity 10.23. 



Addition of sour pasteurized milk. 

 Acidity 9.87. 



Per 



cent of 

 sour 

 milk 



added. 



Acid- 

 ity. 



Alcohol test. 



Per 



cent of 

 sour 

 milk 



added. 



Acid- 

 ity. 



Alcohol test. 



75 per 

 cent. 



68 per 

 cent. 



44 per 

 cent. 



75 per 

 cent. 



68 per 

 cent. 



44 per 

 cent. 



0.0 

 1.0 

 2.5 

 5.0 

 10.0 



1.84 

 1.93 

 2.06 

 2.30 

 2.70 



+M 

 + L 

 +L 



+M 

 + L 

 +L 



+M 







+ S 

 +M 

 +L 



+L 



+M 

 +L 

 +L 



+VS 



1.0 



2.5 



5.0 



10.0 



1.88 

 2.00 

 2.29 

 2.68 



1 See footnote under Table 1. 



In connection with the relation of acidity to the alcohol test the 

 question arises as to whether or not the acidity of a sour milk can be 

 neutralized so that the alcohol test will be negative. Some investi- 

 gators have shown that the neutralization of the acidity does not 

 cause a positive test to become negative, although the size of the 

 flakes in the coagulation is somewhat reduced. We have tried one 

 experiment in which various amounts of normal lactic acid were 

 added to fresh milk, after which the acidity was reduced to the original 

 acidity by the addition of sodium hydrate. From the results which 

 are shown in Table 8 it will be seen that when the acidity was in- 

 creased to 4.3, then neutralized to 1.90, the 68 per cent alcohol test 

 was positive. The positive alcohol tests with 68 per cent alcohol 

 could be made negative at acidities below 4.30 by reducing to about 

 the original acidity of the normal milk. 



